The goal of this research is to understand the molecular physiology of the gonadotropin-releasing hormone (GnRH) and pro-opiomelanocortin neurons. An array of cells in the hypothalamus and forebrain secretes GnRH, which controls the release of pituitary gonadotropins and ultimately coordinates the reproductive axis in both male and female animals. Despite their acknowledged role in reproductive physiology, we understand little about the cell biology of these neurons. Our first objective is to examine the regulation of several important genes coexpressed by GnRH neurons in the rat brain. To this end, we will focus on two proGnRH processing enzymes, carboxypeptidase H (CPH) and alpha- amidating enzyme (PAM), and the neuropeptide galanin. We will test the hypothesis that these genes, as expressed in GnRH neurons, are targets for sex steroid-dependent feedback regulation. Using double in situ hybridization, we will measure and compare cellular levels of the messenger RNAs for CPH, PAM, and galanin in GnRH neurons under different steroid treatment regimens. Other neurotransmitter systems in the brain, including members of the endogenous opioid family (e.g., beta-endorphin from POMC), transduce hormonal signals from the gonads (e.g., testosterone and estradiol) and modulate the secretory activity of GnRH neurons. Our second objective is to learn more about the molecular physiology of testosterone-sensitive POMC neurons in the hypothalamus of the rat. We and others have previously shown that POMC neurons in the arcuate nucleus are functionally heterogeneous, but what molecular attributes determine this heterogeneity and how gene products, in addition to POMC itself, are regulated within these neurons are unknown. We will use double in situ hybridization to measure POMC mRNA and aromatase or estrogen mRNAs for the purpose of studying how these genes are regulated by sex steroids within anatomically defined subsets of POMC neurons. We believe this work will foster understanding of cellular neuroendocrinology and may offer clues to resolving clinical problems related to human reproduction.